Datanode not running and not able start

Question

The datanode daemon is not running:
$ sudo jps
1685 NameNode
1855 NodeManager
3689 SecondaryNameNode
1916 JobHistoryServer
1798 ResourceManager
4029 Jps

I tried to start the datanode using cmd:

/usr/lib/hadoop-2.2.0/bin/hadoop datanode

but it gave below error:
 

WARN datanode.DataNode: Invalid dfs.datanode.data.dir /usr/lib/hadoop-2.2.0/hadoop2_data/hdfs/datanode : 
org.apache.hadoop.util.DiskChecker$DiskErrorException: Directory is not readable: /usr/lib/hadoop-2.2.0/hadoop2_data/hdfs/datanode

Answer 1

Please type the below command in the terminal to solve the problem:

sudo service hadoop-master restart
sudo jps